In the above, I'm using mean mixture fraction polynomial fits. I obtained the coefficients from Fluent. However, when I run my case, the data are off the charts with a minimum of 1.E+8 (which is the default value set by fluent).

So I tried to do it using DEFINE_ADJUST:
DEFINE_ADJUST(udf_critical_strain_rate,d)
{
Thread *t;
cell_t c;